Throwing up is a symptom get a good G.I doctor,vomit is loaded with acid and can cause even more damage I advise you too seek s doctor ASAP
Welcome to the gastroenterology community! Has he ever seen a gastroenterologist about this? Has he ever had any testing done?
He may have food sensitivities. I don't know a whole lot about pediatric food sensitivities, but you could see if there is a naturopath in your area who deals with pediatric patients. They teach people about elimination diets.
You should probably find an allergist who can deal with pediatrics, too. Mine does, and this should be covered by all insurances--unlike naturopathic medicine.